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ATOMIC ENERGY CENTRAL SCHOOL- KUDANKULAM

Handout –Module-3/4

Subject-Chemistry Class-X

Lesson No.- Chapter 1- Chemical Reactions and Equations

Name of the topic – Displacement, Double Displacement, Neutralisation Reaction

Displacement Reaction

ó A single-displacement reaction is a in which one (or more) element(s) replaces an/other element(s) in a compound. It can be represented generically as:

A + B-C → A-C + B

ó Displacement reaction can also be defined as – “More reactive metal displaces less reactive metal from its solution.”

ó Examples- Fe + CuSO 4(aq) FeSO 4(aq) +Cu

ó 2AgNO 3 +Cu Cu(NO 3)2 + 2Ag

ó Zn + HCl ZnCl 2 + H 2 Characteristics of Displacement reaction

ó High reactive metal displaces low reactive metal.

ó The displacement process is slow.

ó In this type of reaction metal displaces other metal from its salt solution.

ó Zn(s) + CuSO 4(aq) → ZnSO4(aq) + Cu(s) (Copper sulphate) (Zinc sulphate) Pb(s) + CuCl 2(aq) → PbCl 2(aq) + Cu(s) (Copper chloride) (Lead chloride)

ó Zinc and lead are more reactive elements than copper. They displace

copper from its compounds.

ó Activity 1.9 NCERT TEXT

ó Experiment -Take three iron nails and clean them by rubbing with sand paper.Take two test tubes marked as (A) and (B). In each test tube, take about 10 ml copper sulphate solution.Tie two iron nails with a thread and immerse them carefully in the copper sulphate solution in test tube B for about 20 minutes. Keep one iron nail aside for comparison. After 20 minutes, take out the iron nails from the copper sulphate solution. Compare the intensity of the blue colour of copper sulphate solutions in test tubes (A) and (B).

ó Observation-The iron nail become brownish in colour and the blue colour of copper sulphate solution fade. Solution’s colour changes to light green

ó Inference - In this reaction, iron has displaced or removed another element, copper, from copper sulphate solution. This reaction is known asdisplacement reaction. Green colour is duet o the formation of ferrous sulphate(Iron (II) sulphate).

Fe(s) + CuSO 4(aq) → FeSO4(aq) + Cu(s) (Copper sulphate) (Iron sulphate)

Double Displacement Reaction

ó A double displacement reaction is a type of reaction in which two reactants exchange ions to form two new compounds. Double displacement reactions typically result in the formation of a product that is a precipitate.

ó Double displacement reactions take the form: AB + CD → AD + CB

ó Examples-Pb(NO 3)2(aq) + 2 KI(aq) → 2 KNO 3(aq) + PbI 2(s)

ó AgNO 3(aq) + NaCl(aq) → AgCl(s) + NaNO 3(aq)

ó FeCl 3(aq) + NH 4OH(aq) NH 4Cl(aq) + Fe(OH) 3(s) Activity 1.10 NCERT TEXT

ó Experiment-Take about 3 mL of sodium sulphate solution in a test tube.In another test tube, take about 3 mL of barium chloride solution. Mix the two solutions.

ó Observation -A white ppt is formed which settles down in a colourless solution.

ó Inference -This insoluble substance formed is known as a precipitate. Any reaction that produces a precipitate can be called a precipitation reaction.

Na 2SO 4(aq) + BaCl 2(aq) → BaSO 4(s) + 2NaCl(aq) (Sodium Sulphate) (Barium Chloride) (Barium Sulphate) ()

Characteristics of Double Displacement Reaction

ó A double displacement reaction is a type of chemical reaction in which the reactant ions exchange places to form new products.

ó Usually, a double displacement reaction results in precipitate formation.

ó The chemical bonds between the reactants may be either covalent or ionic. ó A double displacement reaction is also called a double replacement reaction, salt metathesis reaction, or double decomposition

Neutralisation Reaction

ó A neutralization reaction is a chemical reaction between an and a which produces a more neutral solution.

ó The classic example of a neutralization is the reaction between an acid and a base to yield a salt and :

ó acid + base → salt + water

HCl + NaOH NaCl + H2O

HCl + KOH KCl + H2O

2HNO 3 +Mg(OH) 2 Mg(NO 3)2 + 2H 2O Characteristics of a neutralisation reaction

ó Neutralization is a process when and bases react to form salt and water.

ó The pH of the neutralized solution depends on the strength of acid or base involved in it.

ó If a strong acid is mixed with a strong base then the salt formed is neutral.

ó KOH + HNO 3 KNO 3 + H 2O ó If a strong acid is mixed with a weak base then the acid formed is acidic.

ó HCl + NH 4OH NH 4Cl + H 2O ó If a weak acid is mixed with a strong acid then the salt formed is basic.

ó CH 3COOH + NaOH CH 3COONa + H 2O ó Ionic Equations for Neutralisation reaction

While strong acids and strong bases completely dissociate, weak acids and bases only partially dissociate to form an equilibrium mixture. The neutralization remains incomplete. ó HCl(aq) + NaOH(aq) NaCl(aq) + H 2O(l) ó When equal amounts of a strong acid such as are mixed with a strong base such as , the result is a neutral solution. The products of the reaction do not have the characteristics of either an acid or a base. Here is the balanced molecular equation.

+ - + - + - H (aq) + Cl (aq) + Na (aq) + OH (aq) Na (aq) + Cl (aq) +H 2O ó Chemical reactions occurring in aqueous solution are more accurately represented with a net ionic equation. The full ionic equation for the neutralization of hydrochloric acid by sodium hydroxide is written as follows:

+ - ó H (aq)+ OH (aq) H 2O ó Since the acid and base are both strong, they are fully ionized and so are written as ions, as is the NaCl formed as a product. The sodium and chloride ions are spectator ions in the reaction, leaving the following as the net ionic reaction.

Application of Neutralisation Reaction

ó In the rubber industry, ammonia solution, NH 4OH, is used to prevent the

coagulation of latex because ammonia solution, NH 4OH, can neutralize the acid (lactic acid) produced by bacteria in the latex.

ó Bee stings contain formic acid and are acidic in nature, these stings can be neutralized by applying a base like baking soda.

ó Acidity or gastric problems arise due to an increase of acid in the stomach, Anti-acids or antacids are medicines containing bases such as NaHCO3 () Mg(OH)2 (magnesium hydroxide) neutralize excess of acid in the stomach

ó Most food particles are acidic in nature. For example, lemonade, chocolate, etc. Such foods produce acid in our mouth which reacts with enamel i.e. calcium phosphate and leads to cavities. Using toothpaste while brushing helps to neutralize the acid since toothpaste is a base.